Golf club and manufacturing method thereof

ABSTRACT

A gold club in which the repulsion area of the face portion is shifted downward, and a manufacturing method of such a golf club are provided. The structure of the golf club is such that, in order to shift the sweet area of a face portion having a striking face downward, a crown portion is subjected to an age hardening process to intentionally enhance any one or more of the mechanical qualities of material of the rigidity, strength and hardness of the crown portion. By shifting the sweet area downward, eventually a repulsion effect in the shifted position can be improved, and a ball can be struck without causing a decrease in a traveling distance as in the case when striking the ball on the upper position, even if the striking position is the position shifted to the lower part of the face portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf club and a manufacturing method thereof. In more detail, the present invention relates to a golf club in which rigidity, strength and hardness of the crown portion is enhanced to improve a repulsion effect, and to a method for manufacturing such golf club.

2. Description of the Related Art

Various improvements have been made in golf clubs in order to increase a traveling distance or to achieve a stable strike. The traveling distance directly influences the score, so the traveling distance is increased if scope of a striking point on the head of a golf club is wide, or the position of the scope of the striking point is changed. The striking surface of a golf club is called “clubface”, and a user usually would not try to strike a ball on any parts off the clubface no matter the condition.

On the other hand, recently, golf clubs have been made to have the increased volume at their clubheads in order to increase the area of the sweet area. As a result, repulsive force of the face portion can be increased. Also, by increasing the volume of the clubhead, the center of gravity of the clubhead is raised. For this reason, the center of the sweet area is located in the upper part of the clubface. As a measure for this fact, the center of gravity of the clubhead is lowered by using a method for placing weight on the sole portion, or other methods. However, with this method the clubhead is increased in weight, thus this method is against the request of weight reduction.

The striking point called “sweet area” is located adjacent to the center of gravity, and is the part with which the longest traveling distance can be obtained. For this reason, in a golf club having a conventional configuration, in order to obtain a traveling distance by maximizing the repulsive force that the head has, normally a ball has to be struck with the sweet area which is above the center of the clubface. However, sometimes a ball is struck with a part off the upper sweet area. For example, in a head (against) wind, if the ball is struck in the usual manner, the ball will fly high up in the air and fly against the wind, resulting in a failure to get the desired traveling distance, thus golfers usually strike the ball so as to produce a low ball trajectory. In this case, the striking point is shifted to a lower area of the clubface.

This, however, results in a decrease of the repulsive force and the ball traveling distance becomes less than that obtained by striking on a preferred point of the sweet area. Because the center of gravity is shifted to the position located at the upper side of the club face, as mentioned above, that is, because the sweet area, which is a high-repulsion area, is in the vicinity of the center of gravity, if the striking point is off this area, repulsive force is reduced. Various methods have been suggested as a technology to improve the repulsion effect of the sweet area.

For example, in an example where the crown portion is subjected to some sort of a process, there is a golf club in which a plurality of grooves are provided in the crown portion from the side portion in the toe through the side portion in the heal to raise the angle where the ball is struck and increase the traveling distance (see Japanese Patent Application Laid-open No. 2003-88601), or, a golf club in which the crown portion is provided with a slit which extends along the face portion, and the slit is closed by application of a fiber reinforced plastic as a reinforcing material, to improve repulsion and increase traveling distance (see Japanese Patent Application Laid-open No. 2003-210621).

Further, there are known golf club, such as the one in which an opening portion is formed in the vicinity of the center of the crone portion, the opening portion is closed with a cover material made of a material that is different from that of the head main body, and a reinforcing material made of a fiber reinforced plastic is laminated on the face portion of the head main body to enhance the repulsion while maintaining decay durability (see Japanese Patent Application Laid-open No. 2003-250933), and also the one in which, as an example of combining a foreign material, a fiber reinforced material is used in at least one of the neck portion (hosel portion), face portion, sole portion, crown portion and side portion, such that the mass of the fiber reinforced material becomes 4% or more of the mass of the head main body, and the rest is configured from metal, whereby the golf club has a combination of vibration damping property and hitting sound which is pleasing to the ear (see Japanese Patent Application Laid-open No. 2003-199848).

These conventional examples postulate that repulsion is enhanced to strike a ball far by subjecting the crown portion to some sort of a process to relatively change the strength therein compared to that in the sole portion, and intentionally bending the face portion on crown portion side. In this configuration, the sweet area tends to be shifted toward the upper portion side of the face portion, and this effect is caused when striking a ball on the upper part of the face portion. This manner of striking a ball is usually for pro golfers. However, there are not only pro golfers but also numbers of amateur golfers. Although Amateur golfers have a certain level of golfing skill, they prone to strike a ball in irregular manners.

Therefore, sometimes the striking point is shifted to below the face portion. Even an abovementioned pro golfer strikes a ball on the lower part of the face portion. Specifically, striking a ball on the lower part of the face portion is performed when striking a ball to produce a low ball trajectory in a head (against) wind. For the reason of such a manner of using a golf club, what is desired is a golf club which has a capability for achieving a long ball traveling distance when striking a ball on any point in the face portion, and in which repulsive force equal to that in the conventional sweet area can be obtained as described above even if the sweet area of this golf club is shifted to below the face portion.

Although various methods for solving above problems have been proposed, no technologies have yet been established. The same applicant proposes, as a method for solving the problems, a golf club which has an improved sole portion, and in which striking a ball on a lower part of the sweet area does not result in decrease of a ball traveling distance. This technology is configured by transforming a part of the sole portion.

The above describes a technology for improving a repulsion effect. There is also proposed a technology for reducing a coefficient of rebound, in consideration of the restriction of the limit of the golf rules (see Japanese Patent Application Laid-open No. 2004-49734).

As above, the golf club is designed in various ways to increase a ball traveling distance, but one is not necessarily satisfied with such a golf club under the present circumstances. Especially when expanding the sweet area, or when lowering the sweet area, there is still room for improvement. Although there are some conditions in restriction in manufacturing a golf club, further development of a gold club for increasing a ball traveling distance by one normal strike is desired even in the range of these restriction conditions.

Transforming the crown portion in various ways, transforming the sole portion on the other hand, or other modifications have been tried in the past as described above, and although some effects can be observed in improvement of repulsion in an upper part of the face portion, the effect has not yet been exerted in a lower part of the face portion. These conventional methods still have drawbacks in the reliability, and drawback of even reducing the rigidity by contrast, so not everything was necessarily satisfying. Moreover, the golf industry is a world where tradition is valued originally.

Changing the shape, weight and the like of the clubhead significantly from those of the conventional golf clubs will not only break the rhythm when striking a ball because the swing or the like has to be changed, but also causes an adverse effect. Furthermore, even if an innovative golf club is developed, it takes a long period of time to become popular in the field. Therefore, in a currently popular golf club, significantly changing the shape thereof brings about various obstacles, thus it is ideal to develop a golf club which can satisfy golfers by improving the function without significantly changing the current shape, or without changing the shape at all if possible.

Next, various configurations of a golf club in which the material of the head is changed. As an example of a configuration which is applied to the current golf club, there are known configurations such as one in which different types of metals are applied to the crown portion, hosel portion and the like respectively, and one in which different types of metals as reinforcing materials are bonded together by welding. There is no ideal form of golf club as described above under the present circumstances. Therefore, it is desired to develop a golf club in which the repulsion area is enlarged, shifted or the like without changing the shape thereof significantly from that of the conventional golf club, to stably increase a ball traveling distance even when a ball is struck on any point in the face portion. The same applicant performs various tests in order to solve these problems, to improve the golf club.

As a result, in a golf club in which the crown portion tends to be made weaker than the sold portion in terms of the rigidity and the like, generally a high-repulsion area is shifted toward the crown portion in the face portion. If the striking point is limited to the crown portion side as above, a difficult swing is required for a golfer because the sweet area is narrowed down and whereby the range of the striking point is too narrow to increase a traveling distance. The present invention changes the notion of the conventional golf club, and is designed such that the crown portion is improved in its rigidity, strength, and hardness, and the position of the sweet area is adjusted to the sole portion side to intentionally shift the position.

Moreover, as described above, there is proposed a technology for controlling a repulsion effect, which may be inconsistent with the above description and different from the object of the present invention. For example, there is a technology for subjecting the clubhead of an existing golf club to a heat treatment for age hardening the clubhead. This technology is applied to the face portion, such that the face portion is hardened by age hardening, and the coefficient of rebound is reduced intentionally.

SUMMARY OF THE INVENTION

The present invention is contrived based on the above-described background art, and achieves the following objects.

An object of the present invention is to provide a golf club in which rigidity, strength or hardness of the crown portion is enhanced more than the rigidity, strength or hardness of the sole portion to improve the repulsion effect, and a method for manufacturing such golf club.

Another object of the present invention is to provide a golf club which is configured such that a traveling distance can be increased without changing the basic form at all, and a method for manufacturing such golf club.

Yet another object of the present invention is to provide a golf club which can be produced at low cost, and a manufacturing method thereof.

The present invention takes the following means in order to achieve the above objects.

A golf club of the present invention 1 comprises a face portion which is disposed at a front face of a metallic hollow golf clubhead and has a striking surface for striking a golf ball, and a body portion which constitutes a remaining part of the clubhead other than the face portion, wherein the body portion comprises a sole portion which forms a lower portion of the metallic hollow golf clubhead, and a crown portion which forms an upper portion of the metallic hollow golf clubhead, the crown portion having a structure in which any one or more mechanical qualities of material of rigidity, strength and hardness is intentionally enhanced with respect to the sole portion.

In more detail, in a golf club comprising a face portion which is disposed in a metallic hollow golf clubhead and has a striking surface for striking a golf ball, and a body portion which constitutes a remaining part of the clubhead other than the face portion and comprises a sole portion forming a lower portion of the metallic hollow golf clubhead, a crown portion forming an upper portion of the metallic hollow golf clubhead, a toe portion forming a forepart of the metallic hollow golf clubhead, a heel portion forming a rear part of the metallic hollow golf clubhead, a back portion positioned opposite the face portion and forming a back part of the metallic hollow golf clubhead, and a hosel portion to which a shaft is connected, the rigidity, strength or hardness of the crown portion of the body portion is enhanced compared to that of the sole portion. Consequently, the sweet area of the face portion can be shifted downward.

“Rigidity” used in the present invention refers to an inverse of a proportional constant, the proportional constant being obtained when a load acts on a part of a solid object, and thereby the deformed amount is proportional to the load in an elastic deformation region. “Strength” used in the present invention refers to material mechanical stress such as tension, compression, shearing, bending, and torsion. “Hardness” used in the present invention refers to the amount expressed by the dimension of a resistance when a certain object is pressed against the clubhead. Specifically, hardness means Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness of rebound hardness, and the like as a static impressing hardness test.

In a golf club of the present invention 2, according to the present invention 1, the metals are plates, and the rigidity, strength and hardness of the crown portion are made different by subjecting the plates to a heat treatment.

In a golf club of the present invention 3, according to the present invention 1 or 2, the body portion is obtained by weldbonding the sole portion, the crown portion, and the hosel portion to which the shaft is connected.

In a golf club of the present invention 4, according to the present invention 3, the metals are plates, and the rigidity, strength and hardness are made different by making the materials of the plates different.

A method for manufacturing a golf club of the invention 5 has the step of, in a golf club comprising a face portion which is disposed at a front face of a metallic hollow golf clubhead and has a striking surface for striking a golf ball, and a body portion which constitutes a remaining part of the clubhead other than the face portion, intentionally changing, so as to enhance, any one or more mechanical qualities of material of rigidity, strength and hardness of a metal constituting a crown portion, which forms an upper portion of the metallic hollow golf club and is a part of the body portion, with respect to a sole portion which forms a lower portion of the metallic hollow golf club and is a part of the body portion, and adjusting the position of a sweet area on the striking surface.

The method for manufacturing a golf club of the present invention 6 is, according to the present invention 5, a method in which the metals are plates, and the rigidity, strength and hardness of the crown portion are made different by subjecting the plates to a heat treatment.

In the method for manufacturing a golf club of the present invention 7, according to the present invention 5 or 6, the body portion is obtained by weldbonding the sole portion, the crown portion, and the hosel portion to which the shaft is connected.

In the method for manufacturing a golf club of the present invention 8, according to the present invention 7, the metals are plates, and by differing the materials of the metals constituting the sole portion and the crown portion, the rigidity, strength and hardness of the metals are made different.

In the method for manufacturing a golf club of the present invention 9, according to the present invention 7, the weldbonding is performed by hardening only the crown portion by means of a heat treatment, followed by welding the face portion and each portion of the body portion.

In the method for manufacturing a golf club of the present invention 10, according to the present invention 9, the metal for the crown portion is a metal plate obtained by age hardening a β titanium alloy, and the metal for the sole portion is another metal plate obtained without age hardening the same.

In the golf club of the present invention, as described above in detail, since rigidity, strength, hardness and the like of the crown portion are enhanced more than those of the sole portion, the region of the repulsion area of the face portion is adjusted such that the it is shifted downward. As a result, the repulsion effect in the shifted position is improved. Therefore, even if the striking position is the position to which the repulsion area is shifted downward (lower position of the face portion), as with in the upper position, a golf ball can be sent far without causing a decrease in a traveling distance.

Moreover, since only rigidity, strength, hardness and the like of the metals are changed without changing at all the basic form from the conventional ones, when the golf club is addressed, the outer shape viewed by the player is not different from the conventional ones, and the striking performance is improved with respect to the conventional ones. In production, press working, which is the same step as the conventional production method, can be applied, thus the cost is not increased, the performance can be improved, and the production can be performed in the same way as the conventional production method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an appearance diagram showing the entire boy of the golf club;

FIG. 2 is a plan view of the driver clubhead of the present invention;

FIG. 3 is a front view of the driver clubhead of the present invention;

FIG. 4 is a side view of the driver clubhead of the present invention;

FIG. 5 is a cross sectional view of a configuration of the members used in consideration of production of the driver clubhead of the present invention;

FIG. 6 is an explanation drawing showing another form in which the club face and the crown portion are welded together so as to be parallel to each other;

FIG. 7 is an explanation drawing showing another form in which the club face and the crown portion are welded together so as to be perpendicular to each other;

FIG. 8 is a data diagram showing the sweet area obtained as a result of a test in which only the crown portion is subjected to an age hardening process;

FIG. 9 is a data diagram showing the sweet area obtained as a result of a test in which only the sole portion is subjected to an age hardening process;

FIG. 10 is a data diagram showing the sweet area as a result of a test in which neither the crown portion nor the sole portion is subjected to a heat treatment; and

FIG. 11 is a data diagram showing the sweet area as a result of a test in which both the crown portion and the sole portion are subjected to the age hardening process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described with reference to the drawings. FIG. 1 is an appearance diagram showing the entire boy of the golf club, and shows a driver clubhead. The golf club of the present invention focuses on a metallic hollow golf clubhead. However, in the present embodiment, a driver clubhead is explained as an embodiment. A driver clubhead 1 related to the present invention has a configuration in which it is supported by a shaft A. FIG. 2 to FIG. 4 shows an embodiment of the driver clubhead 1 in the metallic hollow golf club according to the present invention. It should be noted that the figures show the head part only, and other members such as the shaft A are omitted.

FIG. 2 is a plan view, FIG. 3 is a front view, and FIG. 4 is a side view. As shown in the figures, the driver clubhead 1 is constituted by a crown portion 2, which is the upper part, a sole portion 3, which is the bottom part, a face portion 4 on which a golf ball is struck, toe portion 5, which is the front part of the head, a heal portion 6, which is the rear part of the head, a back portion 10 positioned opposite the face portion 4 and forming a back part of the metallic hollow golf clubhead, and a hosel portion 7, which is a member for causing the shaft A to support the driver clubhead 1.

Each section constitutes a divided part which is obtained by assembling a single or a plurality of the sections to form one member in production, and after being subjected to press working, they are integrated by welding or the like. A member during production is constituted by assembling four parts of a face member (first member), a sole member (second member) which has each part of, as the body member, the toe portion 5, heal portion 6 and back portion 10, a crown member (third member) which has each part of the toe portion 5, heal portion 6 and back portion 10, and a hosel member (fourth member).

A plate material is blanked out into a predetermined shape, heated, and press molded. The heating temperature is 400° C. for the face portion 4 and 900° C. for the sole member. After press molded, the component is deburred (trimmed), and then TIG welding is performed. TIG welding is also called “argon welding”, in which a weld rod, which is a deposit metal itself, is used to eject argon gas from the surrounding area of the tungsten electrode to block the molten metal from the atmosphere.

In the present embodiment, the material of the metal is a titan alloy, and is used to join the face member and the sole member by butt welding them, then join the hosel member to them, and thereafter subject the press-molded crown member to TIG welding. In this process, the crown member is subjected to a process for enhancing the hardness, i.e. the age hardening process in the present embodiment, before welding each member. In this manner, the driver clubhead 1 is constituted by welding and integrating the above members.

The face portion 4 has a slight curved surface, and is configured by a plate-shaped material. The area with a maximum coefficient of rebound is a sweet area 9 in the vicinity of a center of gravity 8. Usually, an effective way of sending a golf ball a long distance is to strike the ball at the sweet area 9. Therefore, this are is enlarged, in other words, the high repulsion area is enlarged, or the coefficient of rebound is set high in this portion. It is well known that if the coefficient of rebound is increased, the ball is sent a long distance. The restitution coefficient is an important factor for determining the performance of golf clubs, and a criterion of measurement has been defined by the United States Golf Association (USGA) for the restitution coefficient. The detailed explanation for the criterion is omitted.

Next, an embodiment in which the repulsion area is shifted or the like. FIG. 5 is a cross sectional view which shows a configuration of the members in production of the driver clubhead 1 from the toe portion side. In FIG. 5, the crown portion 2 has a part of the back portion 10 as the crown member (third member). Although not shown, the crown portion 2 also has a part of the toe portion 5 and of the heal portion 6. Similarly, the sole portion 3 has a part of the back portion 10, of the toe portion 5, and of the heal portion 6 as the sole member (second member). The face portion 4 (face member) and the hosel portion 7 (hosel member) are added to the first member and the second member. The driver clubhead 1 is constituted by these four members, where the members are welded to each other.

A titan alloy used in the driver clubhead 1 of the golf club is β titan alloy or α+β titan alloy. This is improved in its strength by heat treatment, and is excellent in workability, ductility, flexibility, strength and the like, and is highly reliable. This titan alloy is applied in the present invention, but only the crown portion is subjected to the heat treatment for performing age hardening.

In the alloy which is subjected to the heat treatment, the elements of the titan alloy to be deposited at low heat is melted without being deposited by rapid cooling, thus it in an unstable condition. These elements try to return to the original stable state over time, whereby crystals of the intermetallic compound are deposited. The crystals is hardened through this deposition. The hardness and the like differ according to the type of the metal, and the an optimal value is determined by adjusting the heating temperature, heating time, cooling time and the like. In the age hardening process, this phenomena is used, and rigidity, strength, hardness, Young's modulus or the like is improved in the crown portion 2.

In other words, the crown portion 2 is caused to have the rigidity, strength, and hardness that are different from those of other parts. If the rigidity is large, or if the hardness if high, bending or distortion is hardly caused physically. As a result, if external force is applied to the face portion 4, the face portion 4 on the crown portion 2 side is not deformed easily. Specifically, intentionally enhancing the rigidity, strength and hardness of the crown portion 2 decreases metallic distortion or elastic deformation of the crown portion 2. As a result, by controlling bending of the face portion 4 as above, the bent area is moved to the sole portion 3 side relatively, whereby the sweet area 9 is shifted to the lower part of the face portion 4. The age hardening is necessary as long as a fracture is not generated on the crown portion 2 even when a striking force is added to the face portion 4.

Through this process, in other words, by enhancing the rigidity, strength and hardness of the crown portion 2 of the driver clubhead 1, the rigidity of the face portion 4 on the crown portion side 2 is increased, and the rigidity of the face portion 4 on the sole portion 3 side is relatively reduced. As a result, rigidity is present in the crown portion 2 side, while there is room for elastic distortion on the sole portion 3 side, and the repulsion area is shifted to the lower part of the face portion 4. In the present invention, therefore, a certain degree of repulsion force is maintained in the position shifted to the lower part of the face portion 4. In this process, the weight of the clubhead does not change, so the center of gravity 8 of the driver clubhead 1 does not change.

The above explanation was about how the hardness of the crown portion 2 is particularly enhanced by means of the age hardening process. As other embodiments, there are methods for hardening by welding, which is shown in FIG. 6 and FIG. 7. In FIG. 6, the crown portion 2 is divided into a plurality of members, and the members are arranged in parallel along the clubface and are welded as indicated by a weld line 2 a. Similarly in FIG. 7, a plurality of members are arranged in a direction perpendicular to the club face and are welded as indicated by a weld line 2 b.

By configuring by welding the members as above, the welded portions are hardened, and the rigidity, strength and hardness of the crown portion 2 can be enhanced. The figures show an embodiment in which the welded portions are welded in a linear fashion, but they may be welded in crossways or in a curved fashion. Further, as another embodiment, ribs may be provided on the inner surface of the crown portion 2, although this is not shown.

For example, in the abovementioned welding example, instead of welding, ribs may be provided in the back face of the crown portion 2, which is also the welding portion. By providing ribs, the rigidity, strength and hardness of the crown portion 2 can be enhanced as described above. Moreover, by changing the thickness, as another embodiment, the crown portion 2 may be created different from other portions. For the metals, a titan alloy is preferred, but an aluminum alloy, stainless, or the like, may be used. If the types of the metals are different for the portions, the portions may be applied with metals with properties appropriate for the portions.

The present embodiment is designed so as to be produced in the scope based on the regulations including the abovementioned criterion of measurement, optimal conditions are considered by conducting a testing, and the position of the sweet area 9 is adjusted and determined. As a result, in the golf club of the present invention, a ball traveling distance can be stably increased without causing a decrease in the traveling distance as in the conventional golf clubs, even if the striking position is in the position shifted to the lower part of the face portion 4. Thus, even if a ball is struck on the striking position which is shifted to the lower part of the face portion 4, an effect of increasing a ball traveling distance can be generated without causing a decrease in the coefficient of rebound, which happens in the conventional golf clubs.

Examples for confirming the effects related to the above-described embodiments are now described hereinafter. FIG. 8 to FIG. 11 are data diagrams of test results of the sweet area, the data diagrams showing comparative examples of the age hardening process. FIG. 8 shows the sweet area when only the crown portion is subjected to the age hardening process, and the other parts are results of other examples where the testing is carried out in the same condition for comparison. FIG. 9 shows the sweet area when only the sole portion is subjected to the age hardening process, FIG. 10 shows the sweet area when neither the crown portion nor sole portion is subjected to the heat treatment, and FIG. 11 shows the sweet area when both the crown portion and sole portion are subjected to the age hardening process.

In each of the above data diagrams, S1 is a line showing the range where the coefficient of rebound is 0.800, and S2 is a line showing the range where the coefficient of rebound is 0.840. As is clear from these data diagrams, only in FIG. 8 where only the crown portion 2 is subjected to the age hardening process, the sweet area 9 is shifted to the lower part of the face portion 4. The degree of the shifting is adjusted and determined by how the balance of strength and the like between the crown portion 2 and the sole portion 3 is determined. As a result, the effects of the present invention are confirmed. 

1. A golf club, comprising: a face portion which is disposed at a front face of a metallic hollow golf clubhead and has a striking surface for striking a golf ball; and a body portion which constitutes a remaining part of the clubhead other than the face portion, wherein the body portion has a sole portion which forms a lower portion of the metallic hollow golf clubhead, and a crown portion which forms an upper portion of the metallic hollow golf clubhead, the crown portion having a structure in which any one or more mechanical qualities of material of rigidity, strength and hardness is intentionally enhanced with respect to the sole portion.
 2. The golf club according to claim 1, wherein the metals are plates, and the rigidity, strength and hardness of the crown portion are made different by subjecting the plates to a heat treatment.
 3. The golf club according to claim 1, wherein the metals are plates, and the rigidity, strength and hardness are made different by making the materials of the plates different.
 4. The golf club according to any of claims 1 to 3, wherein the body portion is obtained by weldbonding the sole portion, the crown portion, and the hosel portion to which the shaft is connected.
 5. A method for manufacturing a golf club which comprises a face portion which is disposed at a front face of a metallic hollow golf clubhead and has a striking surface for striking a golf ball, and a body portion which constitutes a remaining part of the clubhead other than the face portion, the method comprising the steps of: intentionally changing, so as to enhance, any one or more mechanical qualities of material of rigidity, strength and hardness of a metal constituting a crown portion, which forms an upper portion of the metallic hollow golf club and is a part of the body portion, with respect to a sole portion which forms a lower portion of the metallic hollow golf club and is a part of the body portion; and adjusting the position of a sweet area on the striking surface.
 6. The method for manufacturing a golf club according to claim 5, wherein the metals are plates, and the rigidity, strength and hardness of the crown portion are made different by subjecting the plates to a heat treatment.
 7. The method for manufacturing a golf club according to claim 5, wherein the metals are plates, and by differing the materials of the metals constituting the sole portion and the crown portion, the rigidity, strength and hardness of the metals are made different.
 8. The method for manufacturing a golf club according to any of claims 5 to 7, wherein the body portion is obtained by weldbonding the sole portion, the crown portion, and the hosel portion to which the shaft is connected.
 9. The method for manufacturing a golf club according to claim 8, wherein the weldbonding is performed by hardening only the crown portion by means of a heat treatment, followed by welding the face portion and each portion of the body portion.
 10. The method for manufacturing a golf club according to claim 9, wherein the metal for the crown portion is a metal plate obtained by age hardening a β titanium alloy, and the metal for the sole portion is another metal plate obtained without age hardening the same. 